CVE-2026-43815

Executive Summary

CVE-2026-43815 is a memory-corruption vulnerability (CWE-787, out-of-bounds write) in Apple's macOS that is triggered when the system connects to a malicious Apple Filing Protocol (AFP) server. A successful exploit causes kernel memory corruption, and with a CVSS score of 8.8 (AV:N/AC:L/PR:N/UI:R), the impact is rated High across confidentiality, integrity, and availability. All macOS releases prior to Sequoia 15.7.8, Sonoma 14.8.8, and Tahoe 26.6 are exposed, and because the flaw resides in the kernel path of the AFP client (afpfs), success yields the highest privilege tier on the host — full system compromise.

Technical Analysis

The NVD description states that the vulnerability is a buffer overflow addressed with improved bounds checking, and that "connecting to a malicious afpfs server may lead to kernel memory corruption." The afpfs component is the macOS kernel-side Apple Filing Protocol file-system client. AFP is the legacy AppleShare protocol, historically served on TCP port 548.

The defect class is CWE-787 (Out-of-bounds Write). In this class, a program writes data past the end of an allocated buffer. Here, the malformed input is delivered as a server response, and the parsing occurs in afpfs while running inside the kernel. The buffer overflow therefore results directly in kernel memory corruption rather than a user-space crash. Note that the raw facts provided do not name any specific function, packet field, or parsing routine; the description only identifies the vulnerable component (afpfs), the input source (a malicious AFP server response), and the resulting condition (kernel memory corruption). We do not speculate on the exact protocol field or code path.

Key attack-surface characteristics derivable from the data:

• Vector: Network (AV:N) — the client must initiate a connection to the attacker-controlled server. AFP is commonly used for file shares and Time Machine backup destinations, so a user- or system-initiated connection to an untrusted host is the trigger.
• Complexity: Low (AC:L) — no race condition or special preconditions are described; a malicious server responding to a normal connection is sufficient.
• Privileges: None (PR:N) — the attacker needs no credentials on the victim host; they operate the peer server.
• User Interaction: Required (UI:R) — a victim (user or configured service) must connect to the malicious afpfs server.
• Impact: High on confidentiality, integrity, and availability (C:H/I:H/A:H) — consistent with kernel memory corruption that could be steered into code execution, data manipulation, or denial of service (kernel panic).

The patch is described only as "improved bounds checking," i.e., a defensive input-validation fix rather than a memory-layout randomization change. No public PoC, exploit code, or Nuclei template exists as of this report. EPSS is 0.00203 (10.4th percentile), indicating low near-term exploitation likelihood, and the CVE is not in CISA KEV — but kernel code execution warrants prioritized patching because weaponization would be high value.

Exploitation Scenarios

No public proof-of-concept is available. The following attack chain is inferred at the vulnerability-class level (out-of-bounds write → kernel memory corruption) and does not assert specific function names, protocol fields, or code paths beyond those stated in the NVD description.

1. Reconnaissance / target identification. The attacker identifies macOS hosts that will connect to an AFP server they control. This is achieved by operating a rogue or compromised AFP endpoint (e.g., via the legacy AFP service on TCP 548) and waiting for, or inducing, a victim client to connect through a shared link, a configured network share, Time Machine configuration, or a malicious hostname that resolves to the attacker's server.

2. Triggering the flawed class. When the macOS AFP client (afpfs) connects and begins negotiating with the malicious server, the attacker returns a crafted server response. During processing of that response inside the kernel, an out-of-bounds write occurs because the input exceeds what the parser's bounds checking permits. The mechanism is a buffer overflow in the kernel-side AFP client, exactly as the NVD description states.

3. Payload / execution at class level. Because the corruption occurs in kernel memory, a crafted response can overwrite kernel data structures. Depending on the precise layout (not disclosed publicly), this could be leveraged toward kernel code execution or privilege escalation, or it may simply crash the kernel. No specific offsets, structures, or exploitation primitives are detailed in the available data, and none are fabricated here.

4. Post-exploitation impact. Success yields code execution at the highest privilege level on the affected Mac — defeating user-space security controls and undermining system integrity. Even absent full exploit development, reliable kernel memory corruption enables denial of service (forced restart/kernel panic), and untrusted AFP responses can corrupt file-sharing/backup integrity. Because the flaw is client-side, the attacker can target many hosts from a single malicious server without authenticated access to each one.

Impact Assessment

CVE-2026-43815 affects all macOS installations running versions earlier than the fixes in Sequoia 15.7.8, Sonoma 14.8.8, and Tahoe 26.6. The blast radius includes enterprise Mac fleets, mobile workforces, and backup infrastructure wherever AFP shares are still referenced, and any host routinely connecting to third-party or untrusted AFP servers.

Mapping the CVSS subscores: AV:N means the malicious server can be remote and reached across untrusted networks; AC:L means exploitation is reliable without special conditions; PR:N reflects that the attacker needs no privileges on the target; UI:R reflects that a victim must connect to the hostile server; and C:H/I:H/A:H reflects the severe consequences of kernel memory corruption — potential full loss of confidentiality, integrity, and availability of the device. A CVSS of 8.8 places this in the High severity band.

Business impact: a lost Mac can expose credentials, encryption keys, corporate data, and file shares handled by the device. A kernel-level primitive also undermines endpoint protection and may enable lateral movement or persistence if weaponized. Confidentiality loss is the top concern for regulated data; integrity loss threatens backup and file-sharing trust; availability loss materializes as recurring kernel panics.

Detection Guidance

Sigma Rule

title: Potential CVE-2026-43815 Exploitation - AFP Client Kernel Memory Corruption
id: 8f2c1a4e-6b9d-4e7a-9c3f-2d1e5a7b0c44
status: experimental
description: Detects macOS kernel panics and AFP-related crashes consistent with a buffer overflow (CWE-787) in the kernel afpfs client triggered by a malicious AFP server.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-43815
author: valtersit.com
logsource:
  product: macos
  service: system
detection:
  selection_panic:
    message|contains:
      - 'panic'
      - 'Kernel trap'
  selection_afp:
    message|contains:
      - 'afpfs'
      - 'afp'
  condition: selection_panic and selection_afp
falsepositives:
  - Legitimate AFP server faults or hardware issues producing similar panics
level: high
tags:
  - attack.t1203
  - cve.2026.43815

YARA Rule

rule CVE_2026_43815_AFP_Buffer_Overflow_Indicator
{
    meta:
        description = "Heuristic indicator for AFP (afpfs) buffer-overflow artifacts related to CVE-2026-43815"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-43815"
        date = "2026-01-01"
        severity = "high"
    strings:
        $afp = "afpfs" ascii nocase
        $panic = "kernel memory corruption" ascii nocase
        $kern = "Kernel trap" ascii
    condition:
        (uint16(0) == 0x5A4D or uint32(0) == 0xFEEDFACF) and
        (($afp and $panic) or ($afp and $kern))
}

Suricata IDS Rule

alert tcp $HOME_NET any -> any 548 (msg:"CVE-2026-43815 Potential Apple AFP Malicious Server Response (afpfs overflow)"; flow:to_client,established; content:"|00 00|"; depth:2; threshold:type limit, track by_src, count 1, seconds 300; metadata:cve CVE-2026-43815, attack_target Client_Endpoint, created_at 2026-01-01, updated_at 2026-01-01; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-43815; classtype:attempted-user; sid:202643815; rev:1;)

Elastic Detection

process where host.os.type == "macos" and event.category == "process" and
process.name in ("kernel_task") and
process.args : "*afpfs*" and
message : "*panic*"

Splunk SPL Query

index=macos sourcetype=system OR sourcetype=osquery
| search ("afpfs" OR "afp")
| search (panic OR "kernel trap" OR "memory corruption" OR crash)
| stats count min(_time) as first_seen max(_time) as last_seen values(host) as hosts by process, message
| where count > 0

Wazuh OSSEC Rule

<group name="macos,cve-2026-43815,">
  <rule id="202643815" level="12">
    <decoded_as>json</decoded_as>
    <field name="message">afpfs|afp</field>
    <match>panic|kernel trap|memory corruption</match>
    <description>CVE-2026-43815: Possible macOS AFP client (afpfs) kernel memory corruption triggered by malicious AFP server.</description>
    <mitre>
      <id>T1203</id>
    </mitre>
    <group>cve_2026_43815,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 2/4 (CLAIMED — a single source, NVD, claims the patch; it has not been independently confirmed). Treat the fix as available but verify against Apple's own security releases before closing the loop.

1. Immediate mitigations (no patch dependency):

   • Do not connect affected Macs to AFP servers that are not fully trusted and under organizational control.
   • Where AFP is unused, disable or block the legacy AFP service (TCP 548) at the host and network perimeter.
   • Restrict outbound access so managed Macs cannot reach unfamiliar AFP endpoints.
   • Increase monitoring of macOS system logs for kernel panics referencing afpfs.

2. Patch/upgrade steps:

   • Upgrade to macOS Sequoia 15.7.8, macOS Sonoma 14.8.8, or macOS Tahoe 26.6 (or later) as stated in the NVD record.
   • Verify the update against Apple's published security release notes before assuming the claim is confirmed (patch confidence is only 2/4).
   • Reboot to ensure the kernel fix is active.

3. Long-term hardening:

   • Migrate remaining AFP shares to SMB, which is Apple's recommended replacement for AFP.
   • Enforce a strict patch SLA for macOS kernel updates and inventory endpoints so out-of-date versions are visible.
   • Apply least privilege and network segmentation so that even a kernel-level compromise has limited lateral reach.
   • Continuously monitor emerging proof-of-concept activity; EPSS and KEV absence can change once weaponization occurs.

References

• NVD — CVE-2026-43815: https://nvd.nist.gov/vuln/detail/CVE-2026-43815
• Apple Security Releases (macOS Sequoia 15.x, Sonoma 14.x, Tahoe 26.x): https://support.apple.com/en-us/HT201222
• CWE-787 — Out-of-bounds Write: https://cwe.mitre.org/data/definitions/787.html
• MITRE ATT&CK T1203 — Exploitation for Client Execution: https://attack.mitre.org/techniques/T1203/
• FIRST EPSS — CVE-2026-43815 scoring context: https://www.first.org/epss/

Threat-actor context: no exploit code, PoC, or in-the-wild campaign is associated with CVE-2026-43815 in the available data; the CVE is not listed in CISA KEV and EPSS is low (0.00203). Any future KEV listing or public exploit publication should trigger emergency patching. An AFP-specific Internet-exposed host count check via Shodan (port:548) can help scope how many organizations still operate legacy AFP endpoints that could serve as attacker infrastructure.